The present invention relates generally to the production of images on a imaging media, and more particularly, to a method for forming a full color image such that input data relating to an original color image is processed so that an observer of the output image will perceive close color correspondence between the two images.
The actual or perceived quality of an imaging system depends to a large extent upon the degree to which the output appears to match the input image. In the case of a color image reproduction system, wherein an input color image is copied as an output color image, the match between input and output extends to the color content of the image as well as the achromatic subject information. Thus, the various shades and intensities of the different colors must be properly matched. Ideally, the colors of the output image should be indistinguishable from those of the input image.
Copies may be made, for example, on photosensitive material of the type described in U.S. Pat. Nos. 4,399,209 and 4,440,846. For this output media, the output data must be placed in the form of Cyan, Magenta and Yellow. For other types of output devices and media, other forms for the output data will be required.
In order that the output image will properly match the input image for color content, it is necessary to color calibrate the output device to the input device. This is typically done manually and subjectively, performed for each color channel independently. This results in a cumbersome trial and error method, and furthermore results in a proper calibration match only between the particular input and output devices involved. To substitute a different input and/or output device, as might be done in a large color image production system, the calibration must be performed again.
A second problem results from the fact that any input device has a limited gamut or range of colors which it is capable of detecting. At the same time, an output device has a limited gamut of colors which it can reproduce. For a given image reproduction apparatus, the input gamut and output gamut are likely not to be coextensive, and in fact may have substantial areas in which the two do not match.
Often times, this may not be a problem where the input device cannot detect colors which the output device is capable of printing, other than to cause a situation wherein the full range available from the output device is not utilized. More serious is the situation in which an input color is detected, but cannot be reproduced by the output device. Since these particular elements of the image cannot be simply left blank, some decision must be made as to how such information is to be represented. Such determinations can be made empirically for the entire gamut, but this can be a tedious task. Moreover, it becomes quite impractical for an apparatus in which input and/or output devices of different types may be interchanged.
What is needed, therefore, is a method for image processing which is useable in reproducing input information to output image information regardless of the particular input and output devices used. Moreover, such a method should be capable of facilitating the interchanging of input and output devices, and should be capable of compensating for gamut mismatch between the input and output devices selected.